Trace Element Speciation and Deportment: A Review of Current Status and Needs

ACARP has funded an extensive program of work on trace elements, both directly and indirectly through funding provided to the CRC for Coal in Sustainable Development (CCSD). In this report this work is critically reviewed, together with relevant international research. 

The specific objectives of the project were to:

• review research on trace element deportment and speciation, with a focus on impact of technology, and coal properties on deportment and speciation, and the implications for ash utilisation
• develop specific recommendations concerning the need and focus for future work in this area, enabling ACARP to evaluate further funding priorities in the trace element area 

The review considers the impacts of trace metals in the environment, the contribution of coal combustion to atmospheric emissions of these potentially toxic species, and the importance of speciation. It then illustrates the relationship between coal-derived emissions of fine particles and trace elements. The current state of our understanding of the health impacts of fine particles is included, with a particular emphasis on the role of the metals in determining health impacts. It is concluded that a convincing causal link between final particle composition and the health impacts is still uncertain.

Mechanisms for the emission of trace metals are then described, and international data on emissions of these species from full scale plants is summarised. The final section of the review examines the current status of knowledge of trace elements in Australian coals, including:

• Trace metal concentrations and modes of occurrence;
• Chemical transformations
• Trace element capture in air pollution control devices
• Speciation of trace elements
• Trace elements in coal combustion products (CCPs) and environmental impacts

It is concluded that substantial progress has been made, but that trace element release and environmental impacts from coal combustion are complex, and our understanding is limited by the lack of relevant data, and by limitations in analytical techniques for determination of trace element modes of occurrence and speciation.

It is recommended that future work be undertaken in the following areas:

• Trace element concentrations in Australian and internationally-traded coals should continue to be collected and made available though an accessible database. The database should enable access to all the data to enable statistical comparisons. This may require some management of commercial-in-confidence information.
• For determination of trace element modes of occurrence:
• maintain a watching brief on the improvement of techniques for the determination of modes of occurrence of trace elements in Australian coals
• existing techniques have significant limitations so that further determination of modes of occurrence should only be undertaken when a significant advance has been made
• Devise experiments to investigate how coals with different modes of occurrence for selected elements impact on combustion partitioning

Mercury speciation data should be obtained for a range of Australian coals, with a range of coal chlorine contents under full scale operation.

Further characterization of the speciation of target trace elements in emissions and combustion products should be pursued, particularly as new analytical techniques become available.

Continue to develop risk based approaches for assessing environmental impacts of ash disposal and use; these approaches require data on trace element release, dispersion and transport, and ecosystem sensitivity.